Studies have identified links between inherited gene mutations in type IX collagen and the incidence of intervertebral (IVD) pathology in the human. The role of these genetic factors in IVD disorders is largely unknown, but may relate to a compromised matrix that perturbs normal cell-matrix interactions or can not withstand daily "wear and tear". Mice homozygous for a Col9a1 inactivation that express no type IX collagen protein (Fassler et al. '94) exhibit significant IVD degeneration in both nucleus pulposus and endplate regions, changes that mimic key characteristics of human IVD pathology. The primary hypothesis of this proposal is that deletion of type IX collagen promotes IVD degeneration by altering cell-matrix interactions that regulate cell responses to mechanical loading of the IVD. An alternate hypothesis is that the type IX collagen deletion affects IVD cell metabolism through altered nutrient transport secondary to vertebral endplate changes. Studies will be performed to test both primary and alternate hypotheses on the pathogenesis of IVD degeneration in this model. In Aim 1, cell-matrix interactions in IVDs from wild-type (WT) and Col9a1 knockout (KO) mice will be tested using micromechanical methods to quantify extracellular and pericellular matrix strains following compression. Integrin expression, cytoskeletal staining and electron microscopy will also be used to reveal morphological features of cell-matrix interactions to test for differences between WT and KO IVDs. In Aim 2, studies will quantify nutrient diffusion to the IVDs through the bony endplates via molecular tracking, and cell metabolism will be measured using new microdialysis methods. MicroCT will also be performed to quantify endplate morphology for comparison between WT and KO mice. Studies in Aim 3 will quantify the biological response of IVDs to compression in organ culture via gene expression for relevant proteases and inflammatory mediators. Parameters for WT and KO mice will be used to test the hypothesis that mechanical-biological coupling may be affected by altered cell-matrix interactions in this model New work is also proposed to characterize pain-related behaviors associated with the type IX collagen deletion. Completion of this study will reveal the pathways to IVD degeneration in a model system of compromised matrix integrity, that parallel many features of human IVD pathology. Thus, these results will reveal new avenues for intervention in the treatment of human IVD pathology.